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courses:mapreduce-tutorial:step-29 [2012/01/31 12:42] straka |
courses:mapreduce-tutorial:step-29 [2012/02/05 18:23] straka |
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====== MapReduce Tutorial : Custom sorting and grouping comparators. ====== | ====== MapReduce Tutorial : Custom sorting and grouping comparators. ====== | ||
+ | ====== Sorting comparator ====== | ||
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+ | The keys are sorted before processed by a reducer, using a | ||
+ | [[http:// | ||
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+ | ====== Grouping comparator ====== | ||
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+ | In a reduce, it is guaranteed that keys are processed in ascending order. Sometimes it would be useful if the //values associated with one key// could also be processed in ascending order. | ||
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